The present invention relates to utility knife. More particularly this invention concerns box cutter with an autoretracting blade.
In commonly owned U.S. Pat. No. 6,148,520 a box cutter is described having a housing and a blade slide carrying a blade and displaceable longitudinally in the housing between a rear retracted end position with the blade wholly received in the housing and a front extended end position with the blade extending forward from the housing and through an intermediate position. A spring urges the blade slide continuously rearward into the retracted position. An actuator slide is displaceable in the housing independently of the blade slide between a front end position and a rear end position and through an intermediate position and is provided with an externally accessible actuating formation. Another spring urges the actuator slide continuously into the rear position. A seat member on one of the slides is displaceable along a path on movement of the one slide between its end positions and a coupling member on the other of the slides is engageable in the seat member on forward movement of the actuator slide from its rear position into the intermediate position of the actuator slide for pushing the blade slide forward from its rear retracted position to its intermediate position on displacement of the actuator slide from its intermediate position to its front position. The members are disengaged from each other and the coupling member is displaced out of the path of the seat member on displacement of the blade from its intermediate position into its extended position.
Thus with this system the actuator slide is pushed from its rear position into its forward position to move the blade slide from its rear position into its intermediate position. When the blade is then engaged in a workpiece and, as is usual, rearward traction is applied to the knife to cut the workpiece with the blade, the blade is pulled into its forward position. This causes the coupling member to disengage itself from the seat member and move out of its path. When subsequently the blade is freed from the workpiece, its spring will pull it back into the retracted position even if the actuator slide remains in the front actuated position. Thus the blade can be extended, but once engaged in a workpiece will always automatically retract as soon as it is disengaged from the workpiece.
This arrangement has one significant drawback: When the blade is oriented perpendicular to the workpiece surface being cut, there is no significant longitudinal component of frictional force effective on the blade to move it into the extended or outer position. Thus if the user cuts into a box and then, before the blade has been pulled out into the outer position, pivots up the blade to a perpendicular position, or if the user stabs the knife to start with into the workpiece with the cutting edge perpendicular to the workpiece surface, it is likely that the blade and its slide will never even move into the outer position. The blade and actuator slides will remain coupled together so that, even if the tool is separated from the workpiece, the blade will remain extended, creating a serious potential for injury.
It is therefore an object of the present invention to provide an improved autoretracting box cutter.
Another object is the provision of such an improved autoretracting box cutter which overcomes the above-given disadvantages, that is whose blade will move into the outer position even if the knife""s cutting edge is oriented perpendicular to the surface of the workpiece being cut.
The instant invention is an improvement on an autoretracting knife of the above-described type having a housing and a blade slide carrying a blade and displaceable longitudinally in the housing between a rear retracted end position with the blade wholly received in the housing and a front extended end position with the blade extending forward from the housing and through an intermediate position. The blade has an edge directed transversely and exposed outside the housing in the extended position, and a blade spring urges the blade slide continuously rearward into the retracted position. Furthermore, an actuator slide is displaceable longitudinally in the housing independently of the blade slide between a front end position and a rear end position and is provided with an externally accessible actuating formation. An actuator spring urges the actuator slide continuously into the respective rear position. A transversely displaceable coupling member on one of the slides is engageable with the other of the slides for coupling the blade slide with the actuator slide for movement of the blade slide from its retracted position into its intermediate position on displacement of the actuator slide from its rear end position into its front end position and for decoupling the slides from each other and shifting transversely out of a path of the other slide on movement of the blade slide from its intermediate position into its extended position. In accordance with the invention cam formations on the slides displace the blade slide into the extended position on exertion of a transverse force against the blade edge in the intermediate position of the blade slide.
Thus with the instant invention the cam formations will effectively displace the blade into the extended position when any force is exerted transversely against the blade edge. Of course a standard angled cut will be effective as in the prior-art system to pull the blade out, but with the system of this invention of the knife is stabbed into a workpiece with its blade perpendicular to the workpiece surface, and then pulled parallel to this surface, the cam formations will draw out the blade and uncouple the slides for automatic blade retraction when the cut is completed.
According to the invention the formations include at least one surface extending at an acute angle to a longitudinal direction of movement of the blade slide between its retracted and intermediate positions. More particularly the surface is formed on the blade slide.
The cam formations can according to the invention include another surface formed on the housing and extending at an acute angle complementary to that of the blade-slide surface. In this case the blade slide can be formed with a generally longitudinally extending notch having a wall forming the surface. Alternately the formations include a pin projecting transversely from the housing into the notch.
In another arrangement according to the invention the cam formation is constituted by an L-shaped lever on the blade slide.